Antigenic stimulation during HIV-infection leads to a transient but substantial increase in plasma viremia. The antigen-responding population of T cells may therefore be preferentially targeted for infection and the cytopathic effects of viral replication. To investigate the effects of immune stimulation on T-cell repertoire, T cell depletion, pathogenesis and rate of disease progression, we immunized SIV-infected rhesus macaques with conventional antigens (DPT) or super antigens (SEC3). Increased plasma viremia, monitored by QC-PCR, was observed in all animals following antigenic stimulation. To evaluate the effects of immune stimulation on SIV expression and disease pathogenesis, we immunized macaques either prior to, or after establishing SIV infection. Immune activation at the time of primary SIV infection may predispose the host to an accelerated disease course. Five of 6 DPT immunized macaques manifested rapid disease progression despite full seroconversion to SIV in 4 of the 5 animals, compared to 10 rapid progressors among 31 historical controls (p = 0.031; Fisher's Exact Test). We are currently monitoring primary viremia and associated disease progression in the absence of immune stimulation, and these animals will be used to evaluate the effects of repeated immunization with conventional antigens without immunization prior to SIV infection. This work has elucidated factors which appear to influence SIV disease progression and pathogenesis. *KEY*Immune stimulation, SIV, AIDS, Pathogenesis, Macaque